The present invention relates to a method and apparatus for securing a prosthetic limb to the residual limb of an amputee. More specifically, the method and apparatus of the present invention allows an amputee to easily and accurately secure a prosthetic limb to their own residual limb, in a manner that reduces or even eliminates the pistoning movement that may commonly occur therebetween.
While prosthetic limbs have been around in some form for many years, there are still certain difficulties associated with properly affixing a prosthetic limb to the residual limb of an amputee. These difficulties are typically compounded when the prosthetic limb replaces a portion of an amputee""s leg and, therefore, must be able to support the weight of the amputee and remain secured to the residual leg while allowing the amputee to be ambulatory. There are numerous known techniques for securing a prosthetic leg to a residual leg, many of which are described in detail below.
Early prosthetic legs were often equipped with an apparatus having a belt strap(s) that extended from the top of the prosthetic leg. The belt strap(s) was designed to engage a belt worn around the amputee""s waist. Thus, once the prosthetic leg was in place, the belt strap(s) could be pulled tight and secured to the waist belt. This method did not, however, provide satisfactory results, as the apparatus proved to be quite cumbersome, and a loosening of the prosthetic leg often occurred due to slippage of the belt strap(s) or a sagging of the belt around the amputee""s waist.
Systems have also been developed that allow the residual leg of an amputee to be secured within a receiving cavity of a prosthetic leg via suction created therebetween. It is possible to design such a system so that a very secure initial fit can be accomplished. The drawback to a pure suction system, however, is that any fluctuations in the size of the residual leg can cause a loss of suction, thereby resulting in a less secure fit between the limbs. This has proven to be a common problem with such systems, as the residual leg may often shrink or swell throughout the day as the amputee engages in physical activity. Also problematic is the fact that a residual limb may change shape from day to day for a variety of reasons.
There also exist specialized socks or liners that fit tightly over a residual leg and are adapted to engage with a corresponding prosthetic leg. In one such liner, a cup having a downward protruding pin or screw is provided in the bottom portion thereof. The amputee places the liner on the residual leg and inserts the residual leg into a receiving portion of a prosthetic leg. As the residual leg becomes seated in the prosthetic leg, the pin or screw engages a receiving aperture therein. The aperture may allow the liner to be secured to the prosthetic leg by, for example, threading thereto, or by an interlocking arrangement.
In another version of a liner securing system, a prosthetic leg may have a lanyard passing through the bottom of a residual leg receiving portion thereof. The lanyard may have a threaded element or some other attachment means affixed to one end, so that the lanyard may be releasably connected to a bottom portion of a liner, such as to a cap or cup. In this system, the liner is placed over the residual leg, and the lanyard is attached thereto. As the residual leg is inserted into the prosthetic leg, the segment of the lanyard that extends outside the prosthetic limb can be pulled on by the amputee to assist in ensuring full insertion of the residual leg into the prosthetic leg. Once the residual limb is fully inserted into the prosthetic leg, tension may be maintained on the lanyard and the lanyard may be secured to a belaying cleat or similar retaining device located on the prosthetic limb. The tension of the lanyard against the bottom of the liner then aids in maintaining the position of the residual leg within the prosthetic leg.
As can be seen, there have been numerous attempts at providing a system for securely retaining the residual leg of an amputee within a prosthetic leg. Each of these known systems has drawbacks or deficiencies, however. For example, the security provided by the belt strap and waist belt system is inadequate and has proven uncomfortable to the wearer thereof. As previously mentioned, any changes in the size of the residual leg can have adverse effects on a suction system, as such a system relies on a very close fit between the residual leg and prosthetic leg to maintain a vacuum therebetween. Suction systems also are problematic, in that somewhat embarrassing sounds may be generated thereby both during insertion of the residual leg into the prosthetic leg and during movement of the amputee. These sounds are typically created as small amounts of trapped air escape through gaps between the residual leg and the prosthetic leg. Each of the presently known liner securing systems are also inadequate. The former liner system requires that a securing pin or screw on the bottom of the liner be guided into an engaging feature in the bottom of the receiving cavity of the prosthetic leg. This must be accomplished without the ability to see the engaging feature or the securing pin or screw, as insertion of the residual leg into the prosthetic leg blocks the view of each. The latter liner securing system requires that the amputee have significant hand/arm strength in order to pull the lanyard taut and to maintain the tautness as the lanyard is secured to the belaying cleat. Any slack that develops in the lanyard during this process will result in a less than adequate securing of the residual leg to the prosthetic leg. Such a process can be quite difficult, especially for an elderly and/or arthritic person who lacks the requisite hand/arm strength.
One consequence that results from the inability of the above-described systems to adequately secure a residual limb to a prosthetic limb is that at least a small amount of movement commonly occurs therebetween. In the context of its occurrence between a residual and prosthetic leg, this movement is commonly referred to as xe2x80x9cpistoning.xe2x80x9d Although such pistoning may only involve movement of the residual leg within the prosthetic leg on the order of fractions of an inch, it is nonetheless uncomfortable for the user, and may further impart a feeling of instability. Further, friction caused by this pistoning commonly wears away the material of the liner that is typically placed over the residual legxe2x80x94the result being that the liner must be discarded.
From the foregoing description of the known systems, it can be seen that there is a need for a system and method for easily and adequately securing a residual limb to a prosthetic limb. The system and method of the present invention satisfies this need. The system and method of the present invention allows an amputee to easily fit a prosthetic limb to their residual limb and to securely affix the prosthetic limb thereto. While the system and method of the present invention can be applied to a variety of artificial limbs, for purposes of illustration the system and method will be described herein only with respect to its application to a prosthetic leg.
One exemplary embodiment of the system and method of the present invention described herein, utilizes a lanyard that passes through substantially the bottom of a receiving cavity of a prosthetic leg to secure an amputee""s residual leg thereto. A liner is placed over the residual leg before the residual leg is inserted into the prosthetic leg. The liner is preferably provided with a specialized bottom portion that is designed to engage a receiving device located in the receiving cavity, and is further adapted for attachment to one end of the lanyard. Prior to entering the bottom of the receiving cavity, the lanyard travels through a ratchet mechanism that is located between the receiving cavity portion of the prosthetic leg and the lower portion of the prosthetic leg. When installing the prosthetic leg, the amputee releasably connects the coupling element to the liner prior to inserting the residual leg into the receiving cavity. During this time, the ratchet mechanism is set to allow the free movement of the lanyard therethrough, or is otherwise set to allow ratcheting of the lanyard toward the liner. After connection of the lanyard to the liner, the ratchet mechanism is set to the engaged, or ratcheting (tightening) position, whereby the lanyard may only travel therethrough in a direction that encourages the insertion of the residual leg into the receiving cavity. A suction cup may provided as part of the receiving device that is located in the receiving cavity to accept the distal end of the residual leg. The lanyard may be withdrawn from the receiving cavity by the amputee such that distal end of the residual leg is pulled into secure abutment with the suction cup. The position of the residual leg within the prosthetic leg is then positively retained by the tension of the lanyard, which tension is maintained by the ratchet mechanism.
The system and method of the present invention provides for an easier and more secure installation of the prosthetic leg to the residual leg than is possible with known systems. The ratchet mechanism allows the lanyard to be withdrawn in small increments if desired, without having to maintain a tensile force on the lanyard. The increments are generally detectable by both feel and sound. Because the ratchet mechanism prevents the lanyard from being drawn back into the receiving cavity, the position of the lanyard can be maintained even if the end thereof is released by the amputee. Continuous tension on the lanyard by the amputee is not required, and it is also not necessary that tension be maintained thereon while the lanyard is fastened to a securing feature on the prosthetic leg, such as a belaying cleat. Thus, the ratchet mechanism allows the residual leg to be drawn into the prosthetic leg and secured thereto even if the amputee lacks the hand/arm strength necessary to use a known lanyard securing system.
The ratchet mechanism of the present invention also provides for a more secure fit of the residual leg with the prosthetic leg than has been heretofore possible. Because the ratchet mechanism will not allow the lanyard to be drawn back into the receiving cavity of the prosthetic leg, the position of the prosthetic leg is better maintained during the ambulatory activities of the amputee. Further, the ratchet mechanism eliminates the need for the amputee to maintain tension on the lanyard while securing the lanyard to the prosthetic legxe2x80x94thereby reducing the possibility of an insecure fit due to the amputee allowing the lanyard to slacken during the securing thereof. As a result of using the system and method of the present invention, the above-described pistoning of the residual leg can be reduced or even eliminated. Further details regarding the system and method of the present invention can be ascertained by observation of the following drawing figures and detailed description.